The control of a well may be lost accidentally during drilling or during production. When this happens, the well starts to blow wild, usually catching fire. Because economic and environmental loss occur at an increasing rate during the duration of a blowout, great effort is expended in trying to control the well. This usually involves drilling one or more relief wells. That is, another well is drilled at a safe distance away, which is intended to intersect or come within an effective distance of a lower section of the blowout well so that mud can be pumped into it to prevent flammable formation fluid from reaching the surface.
It will be appreciated that a relief well must be drilled with great directional accuracy in order for it to get within an effective distance of the blowout well. For example, the relief well may be drilled as far away as 1000 feet, or more, from the blowout well, whose borehole diameter is usually about one foot. Further, the blowout well was most likely directionally drilled, thus making intersection even more difficult.
Directional data may not be available on the blowout well, or even if it is, the trajectory of its borehole may not be known with sufficient accuracy to easily intersect it. Various systems have been developed to determine the location of a blowout well from the relief well. While most of them rely on in situ measurements, they usually require that the borehole of the blowout well contain a magnetic material, such as steel. This is because most in situ tools for locating blowout wells are designed to indicate the location of a magnetic material.
Consequently, there exists a need in the art for improved methods and apparatus for intersecting, or coming within an effective distance of a blowout well, in order to kill it. This is especially so when the borehole of the blowout well does not contain a mass of magnetic material, such as a drill stem.